A scale model of a turbofan engine exhaust nozzle is mounted in the Channel 11  dual flow thrust stand. Acoustic data are collected on several channels simultaneously with the thrust and performance measurements.  Each measurement channel consists of a 1/4”  microphone and power supply with analog signal conditioning for filtering and amplification. The data are digitized using a 12-bit A/D converter and stored in binary form for subsequent processing.

Spectral results are obtained from a digital Fourier transform (FFT) producing a narrowband line spectrum. These results are converted to 1/3 octave form by integrating between the prescribed frequency limits for each center frequency. Both the narrowband spectra and the 1/3 octave spectra are saved as text files.

Microphone array

“A Nozzle Test Stand for Simultaneous Measurement of Thrust and Radiated Noise,” D.F. Long, AIAA paper 98-3108, July, 1998. (available on request)

Exhaust nozzle model

Spectral results